International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Volume 3 Issue 1, January 2014 www.ijsr.net Efficient Designing of Communication Link with PSK Modulation using Adaptive Equalization Shalini Garg 1 , Pragati Kapoor 2 1,2 Lingaya’s University, Faridabad, Haryana, India Abstract: In the era of revolution of communication, bandwidth is definitely one of the scarier thing. So the pressure is to reduce the requirement of bandwidth while reduction in bandwidth may result in Inter Symbol Interference. One of the ways to reduce Inter Symbol Interference is to use equalization and in this paper, we have proposed decision feedback equalizer with adaptive equalization for reducing inter-symbol interference and from the depicted results it it quite obvious that the ISI reduces drastically by using adaptive equalization. Keywords: PSK modulation, Equalization, Inter-symbol Interference (ISI), Adaptive Equalization, Frequency-Flat Fading 1. Introduction This Inter Symbol Interference will be one of the common and most effective noise source when we will receive the signal at receiver and in case of a digital signal this will produce lots of error. The reason behind this ever increasing Inter-symbol Interference (ISI) is that, if want to reduce bandwidth of signal beyond a limit channel will definitely become unable to carry information. To minimize this effect, we have to increase time per bit but then this will reduce data speed or the next bit will affect the previous one and create Inter Symbol Interference. Even if we manage these problems there are other sources of Inter Symbol Interference and those are beyond control as these occurs during transmission of signal through channel like multipath time we can negotiate at the receiver minimize their effect but cannot eliminate them. This multipath time occurs because of propagation of a signal through different propagation paths. These paths may vary in length and medium and because of these variations same signal may arrive at a receiver at different time intervals and may be added to the original signal and create Inter Symbol Interference. The ISI may be reduced by using equalization and there are many methods of equalization. 2. Types of Equalization There are two types of equalizer 2.1 Linear Equalizer Linear Equalizers can be used where noise from neighboring channels cannot affect channel and costing is of primary importance a) Mean Square error equalizer b) Zero Forcing Equalizer The Zero-Forcing Equalizer are designed on the basis of maximum distortion at the start of session and this cannot be changed. It can not include the effect of positive additive Gaussian noise effect in the channel. In such type of equalizer problem of noise at high frequency will be more if at the time of designing ISI and channel noise is not considered The Minimum Mean Square error equalizer overcomes this drawback by the equalizer characteristics such that the combined power in the ISI and the additive noise at the equalizer output is minimized 2.2 Non Linear Equalizers These equalizers are very useful in the cases like wireless channels where inter symbol interference is very much possible from neighboring channels and it is varying continuously changing so we cannot design it at the start of session so we have to make changes continuously. 2.2.1 Adaptive Equalizers As in any Feedback System in a adaptive equalizer has two parts one is Forward path and another is Feedback path. The Feedback path provides the output data to a equalizer so that it can compare the output and input. Figure 1 shows the equalizer without feedback. Figure 2 contains a weighted and cascaded Decision along with feedback filters. 2.2.2 Weighted Equalization There are two types of weighted equalizers a)Fixed Weight Equalizers- These equalizer normally used for the cases where frequency response of the channel is constant. In such type of system once the weights fixed it cannot be changed. b)Adaptive Weight Equalizers- These systems are used where frequency response vary with time. In these systems the output of the system is compared with the reference sequence and output varied time to time. Figure 3 shows adaptive fixed equalizer. Adaptive equalizers works in two methods either the receiver information is used to generate error signal or a reference training bits are used which is compared to a known transmission bit sequence and thus if there is any change in timing of bit it can be corrected by calculating the difference between the initial time calculated by training bit. Adaptive equalizer initially produces some error because equalizers try to get used to it. Paper ID: 02013815 346